Semiconductor devices include a plurality of circuit components (i.e., transistors, resistors, diodes, capacitors, etc.) connected together to form an integrated circuit fabricated on a semiconductor substrate. A complex network of semiconductor integrated circuit interconnects (interconnects) are routed to connect the circuit components distributed on the surface of the substrate. Efficient routing of these interconnects, across semiconductor devices, requires formation of multi-level or multi-layered patterning schemes, such as single or dual damascene interconnect structures.
An interconnect structure includes metal vias that run perpendicular to the semiconductor substrate. The metal vias are disposed in trench areas. In addition, an interconnect structure includes metal lines that are disposed in the trench areas, wherein the trench areas are formed in dielectric material. The metal vias are connected to the metal lines, and the metal lines run parallel to the semiconductor substrate. Thus, both the metal lines and metal vias are disposed proximately to the dielectric material having a dielectric constant of less than 5.0, which enhances signal speed and minimizes signal crosstalk (i.e., crosstalk refers to a signal being transmitted through a metal line, and affecting another signal being transmitted through a separate metal line, and/or affecting other parts of circuitry in an undesired manner).
Furthermore, interconnect structures that are copper (Cu) based, when compared with aluminum (Al) based interconnect structures, provide higher speed signal transmission between large numbers of transistors on a complex semiconductor chip. Accordingly, when manufacturing integrated circuits, copper (i.e., a metal conductor) is typically used for forming the semiconductor integrated circuit's interconnects because of copper's low resistivity and high current carrying capacity. Resistivity is the measure of how much a material opposes electric current, due to a voltage being placed across the material. However, when copper is utilized to form interconnects electromigration may occur. Electromigration can result in void formation, as well as extrusion/hillock formation. Integrated circuit manufacturers generally have electromigration requirements that should be satisfied as part of an overall quality assurance validation process, but thereafter electromigration may still persist during the lifetime of an integrated circuit in a user's computer (i.e., when current flows through the semiconductor integrated circuit's interconnect structure).
Specifically, electromigration is the gradual displacement of atoms of a metal conductor, due to high density of current passing through the metal conductor, and electromigration is accelerated when the temperature of the metal conductor increases. Since a semiconductor integrated circuit's interconnect structure is generally formed using copper, which is a metal conductor susceptible to electromigration, electromigration presents a problem when utilizing integrated circuits with copper based interconnects.
Electromigration (i.e., the gradual displacement of metal atoms from one location to another location throughout a metal conductor, due to the high density of current flow) can result in void formation, as well as extrusion/hillock formation in a semiconductor integrated circuit's interconnect structure. The voids can result in an open circuit if one or more voids formed are large enough to sever the interconnect structure, and the extrusions/hillocks can result in a short circuit if one or more extrusions/hillocks are sufficiently long to form a region of abnormally low electrical impedance. Accordingly, void formation and extrusion/hillock formation, due to electromigration, can reduce integrated circuit performance, decrease reliability of interconnects, cause sudden data loss, and reduce the useful life of semiconductor integrated circuit products.